Lipoprotein lipase (LpL), the primary enzyme responsible for the hydrolysis of triglyceride within lipoproteins, modulates plasma levels of all plasma lipoproteins and allows cellular uptake of fatty acids to be used for energy, storage, and structural lipids. This application has funded experiments that have used in vivo methods to define structure/function aspects of LpL biology and assess the effects of tissue specific LpL overexpression. More recently, the PI and his colleagues have produced tissue specific deletion of LpL to investigate the role(s) of this enzyme in heart and skeletal muscle, islet cells, and brain. In addition, funds from this grant were used to create mice with transgenic overexpression of diacylglycerol acyl transferase 1 (DGAT1) in heart and skeletal muscle, and to study animals with a genetic or pharmacologic deficiency of DGAT1. In our Preliminary Results we show the following: muscle overexpression of LpL on a knockout background, but not adipose-specific LpL deletion retards adipose tissue development and increases muscle mass; in the heart, lipid uptake pathways for VLDL and chylomicrons differ; DGAT1 deletion increases muscle mass and also dramatically reduces expression of lipid uptake and oxidation genes. This renewal contains experiments that seek to use modulation of LpL and DGAT1 as tools to understand the following: 1) how tissues deficient in LpL acquire circulating lipids and develop normal adipose triglyceride stores, 2) how muscle lipid metabolism alters skeletal muscle growth, 3) how extracellular and intracellular pools of lipid modulate fatty acid uptake and oxidation via actions of PPARs. The experiments will use novel genetically modified mice, cultured myocytes, and state of the art lipidomics.